Starting with Catel 2.0, it is possible to use the logic of the following controls as a behavior:

• DataWindow => WindowBehavior
• UserControl => UserControlBehavior
• Page => NavigationPageBehavior

This means that you no longer have to derive user controls from the UserControl to use the ability to solve the nested user controls problem. Or, if you are not happy with the endless possibilities of the DataWindow, why not just creating a custom one without having to think about the MVVM integration.

WindowBehavior

The WindowBehavior class takes care of all the MVVM integrations of a window and a view model. So, where you previously had to derive a Window implementation from DataWindow, you can now create a new Window like any application and then add this:

The Save and Cancel properties are not obligate, and need the format of [controlname].[event]. By default, the Click event is used, so if a button (or another control that should respond using the Click event), the [controlname] is sufficient.

<i:Interaction.Behaviors>
    <catel:WindowBehavior ViewModelType="viewmodels:DemoWindowViewModel" Save="okButton.Click" Cancel="cancelButton.Click" />
</i:Interaction.Behaviors>

Seems too easy right? Well, it is really all you have to do.

This looks great, but why is there still a DataWindow with this terrific solution?

First of all, we have to think about all the people that are already using Catel. We don't want to break their code and provide backward compatibility. Updates to the logic will be applied to both the behavior and the view base because the logic is located in a separate class. Also, the DataWindow is truly a terrific class, which supports lots of customization and takes care of dumb generation of buttons and the InfoBarMessageControl.

UserControlBehavior

The UserControlBehavior class takes care of all the MVVM integrations of a user control and a view model. So, where you previously had to derive a UserControl implementation from UserControl, you can now create a new UserControl like any application and then add this:

<i:Interaction.Behaviors>
    <catel:UserControlBehavior ViewModelType="viewmodels:DemoWindowViewModel" />
</i:Interaction.Behaviors>

This looks great, but why is there still a UserControl with this terrific solution?

First of all, we have to think about all the people that are already using Catel. We don't want to break their code and provide backward compatibility. Also, the UserControl implements the IViewModelContainer interface which allows chained view models in a hierarchy. If you don't need this, just go for the behavior. If you need hierarchy chains, either let the custom UserControl implement it or use the UserControl.

To support nested user controls and their validation, it is important to chain views together using the IViewModelContainer interface. You can choose not to do this, but then it is important to disable SupportParentViewModelContainers for performance reasons (otherwise, the behavior will keep searching the visual tree for the parent view model).

NavigationPageBehavior

The NavigationPageBehavior class takes care of all the MVVM integrations of a page (used in navigation or browser based applications) and a view model. So, where you previously had to derive a Page implementation from Page, you can now create a new Page like any application and then add this:

<i:Interaction.Behaviors>
    <catel:NavigationPageBehavior ViewModelType="viewmodels:DemoWindowViewModel" />
</i:Interaction.Behaviors>

This looks great, but why is there still a Page with this terrific solution?

First of all, we have to think about all the people that are already using Catel. We don't want to break their code and provide backward compatibility. Also, the Page class comes with more default functionality that you might be interested in.